The present invention generally relates to the measurement of an unknown capacitance of a capacitive device.
Translational systems are used in digital cameras, video recorders, mobile phones, personal digital assistants, and other electronic devices. These translational systems are used to move mechanical systems (for example, a lens assembly) under an electrical control such as auto-focus or optical image stabilization. In such a translational system, a driver integrated circuit generates a drive signal to an actuator, which in turn drives a mechanical system. The driver generates the drive signal in response to an input command that indicates the desired position of the actuator.
An example of an actuator is a MicroElectroMechanical System (MEMS) actuator. A MEMS actuator typically exhibits a non-linear relationship between the amount of current or voltage applied to it and the amount of displacement it produces. MEMS actuator responses also may vary among manufacturing lots of the same MEMS actuator design. Furthermore, operational factors such as temperature and physical orientation with respect to gravitational force may have a substantial effect on the MEMS actuator responses. Consequently, an open-loop controlled MEMS actuator may not reach the desired position prescribed by the input command, leading to inaccurate performance.
A closed-loop control may be used to drive a MEMS actuator such that the closed-loop control corrects for any error between the desired position and the actual position of the MEMS actuator. A closed-loop control, however, employs a feedback signal that represents the actual position of the MEMS actuator. However, the position of a MEMS actuator cannot be directly measured.
Therefore, the inventors recognized a need in the art for measuring the position of a MEMS actuator.